126 



THE PINEAL ORGAN 



certain fishes and carni- 



the rods as in the eyes of many vertebrates, e.g. 

 vores, also the horse and ox. 



The position which the refractile body (rod or cone) bears to the 

 nucleus of the cell is probably not of so much importance with regard to 

 the reception and transmission of impulses through the cell as one might 

 be led to infer from the examination of specimens prepared with nuclear 

 stains such as hsematoxylin : these give the impression of the nucleus 

 being an opaque, dark, oval body lying in the substance of clear cytoplasm, 



Fig. 88. 



Above — side view of two spiders, Salticus scenicus, showing the four pairs of 



eyes. 

 Below — female of the same species more highly magnified, viewed from in front. 

 (After F. P. Smith, By-paths in Nature.) 



whereas in living tissues the nuclei of cells are transparent and probably 

 would not interfere greatly with the passage of light through them to reach 

 a refractile body or rhabdite situated deep to or beyond the nucleus. 



In the central eyes of the scorpion a refractile vesicle or phasosphere 

 lies deep to the nucleus of each retinal cell, while superficial to it, that 

 is, nearer the lens, is a well-developed rhabdite, and it is probable that 

 rays of light traversing the cell would be refracted by both these bodies 



